Semiconductor integrated circuits (ICs) are manufactured using complex and time consuming processes to fabricate a wafer having large numbers of individual IC “chips”. Semiconductor chips are tested individually or in wafer form. Contact surfaces (e.g., bond pads) are electrically contacted on the chip and connected via a probe device to test equipment (e.g., a test circuit). Electronic test signals are applied to the circuit on the chip via the test equipment and the probe device, and the response to these test signals is measured and evaluated.
Differential circuits are more difficult to design and test than typical single-ended circuits, particularly when such differential circuits are designed to process signals carried on radio and microwave frequencies. For example, some automotive radar systems use differential circuits that process signals at microwave frequencies. Electrical metrology and characterization of these devices is problematic at frequencies around 80 GHz, particularly if differential signals are supplied to or received from a device in wafer level testing. Due to the tolerances of cables and connectors, conventional approaches for testing such devices are not viable at higher microwave frequencies since imperfections adversely affect the ability to establish the 180° phase relation between the differential signal components with the desired accuracy.